| 摘要 |
PURPOSE:To detect surely a bell signal by providing a bell ringing block circuit in series with a bell connected in series with a DC blocking capacitor to inhibit the ringing of bell until a bell signal circuit produces an output. CONSTITUTION:When a bell signal for incoming and talking is transmitted from an exchange via lines L1, L2, the signal is incoming to a series circuit comprising a bell 4 and a bell ringing block circuit 10 via a hook contact (a) and a capacitor 5 and also inputted to a bell signal detecting circuit 6. The bell signal detecting circuit 6 produces an output with a delay of time td so as to bring a loop control circuit 2 in the state of loop forming via a control circuit 7. The bell ringing block circuit 10 inhibits the ringing of bell until a time T longer than the said time td is elapsed. When the time T is elapsed and the bell rings, the line L1 is connected to a contact (b) by hooking up, teh ringing of the bell is stopped and the talking is started by a talking circuit 3. Thus, the bell signal is detected surely and ringing at hook-on is prevented. |
